The Galilean moons
The Galilean moons
When Galileo Galilei pointed his hand-held telescope at Jupiter on 7 January 1610, he saw first three, then four small dots near it, whose position changed night after night; he had discovered the first moons orbiting around another planet. He described them in his 'Sidereus Nuncius', later they were named 'Galilean moons' in his honour. The moon Io, coloured yellow by volcanic sulphur, is the innermost of the four satellites, followed by Europa (right), whose diameter of 3122 kilometres is about the same as that of Earth's moon. Ganymede (left), with a diameter of 5262 kilometres, is the largest moon in the Solar System, and Callisto (second from left) is the third largest satellite after Saturn's moon Titan.
Credit:
NASA/JPL/DLR